Question: Determine how many solutions exist for the system of equations. ${-x+y = 7}$ ${y = 7+x}$
Solution: Convert both equations to slope-intercept form: ${-x+y = 7}$ $-x{+x} + y = 7{+x}$ $y = 7+x$ ${y = x+7}$ ${y = 7+x}$ ${y = x+7}$ Just by looking at both equations in slope-intercept form, what can you determine? ${y = x+7}$ ${y = x+7}$ Both equations have the same slope and the same y-intercept, which means the lines would completely overlap. ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ Since any solution of ${-x+y = 7}$ is also a solution of ${y = 7+x}$, there are infinitely many solutions.